In the recent advanced information-based society, in order to achieve high-speed transmission of large-volume data, application systems, such as an information-communication apparatus, that utilize electromagnetic waves in high-frequency bands ranging from a microwave region of 1 to 30 GHz to a millimeter-wave region of 30 to 300 GHz have been proposed to date. For example, there is proposed a system utilizing millimeter waves such as a radar apparatus for measuring inter-vehicle distances.
Such a system utilizing electromagnetic waves of high frequencies employs a high-frequency circuit. As a problem encountered in the field of high-frequency circuit technology, the frequency of a signal for use is so high that impedance mismatch occurs in the parts of connection between high-frequency components, thus causing significant high-frequency signal reflection. For example, in a bonding wire used to provide electrical connection among a semiconductor device, a package, and a wiring board, the higher the frequency of a high-frequency signal to be transmitted becomes, the larger the reactance resulting from inductance components becomes. Therefore, in the case of connecting a high-frequency component such as an MMIC (Microwave Monolithic Integrated Circuit) with a 50Ω transmission line by the bonding wire, impedance mismatch occurs in a connection portion, thus causing significant high-frequency signal reflection.
As a technique to achieve a reduction in reflection in such a connection portion, for example, in a semiconductor package described in Patent literature 1, a stub is disposed in an air space between an end of the semiconductor package and an end of a circuit board to achieve impedance matching.
Moreover, in a high-frequency circuit described in Patent literature 2, a coplanar line having a narrow portion and a broad portion is formed, and a filter is formed by connecting a bonding wire to this coplanar line. In this construction, the line parameters of the narrow portion and the broad portion are determined, using a transfer matrix, so that impedance matching can be achieved in respect of the connected lines at the input end and the output end of the filter.
However, even if an impedance matching circuit is provided by determining pattern configurations and dimensions of transmission lines in a way as shown in Patent literatures 1 and 2, in a step of forming the transmission lines including the matching circuit, variations in dimension of line patterns constituting the matching circuit occur, with consequent deviations of the dimensions of the manufactured circuit from designed values. This gives rise to impedance mismatch.